Marine umbilicals are used to transport materials and information between a control or processing facility such as a platform, surface vessel, or land-based installation, and an undersea oil wellhead. The umbilicals comprise a plurality of inner tubes encased in an outer casing. The inner tubes may independently convey materials such as hydraulic fluids, organic solvents such as methanol, corrosion inhibitors, hot water, etc. from the surface to the wellhead. The solvents and hot water may be used to remove asphaltines, waxes, tars, and other contaminants accumulated on the walls of well pipes. Other inner tubes may provide a conduit for communication cables such electrical and electronic cables or fiber optic cables.
Umbilicals often comprise internal steel tubes encased in an outer polymeric pipe, where the steel tubes are used to convey chemicals such as hydraulic fluids, organic solvents, hot water, and the like. Although steel can be resistant to the chemicals and any elevated pressures used, it can have the disadvantages of high cost, high weight, and poor flexibility and fatigue strength. Flexibility and fatigue strength are particularly important in applications where the umbilical is subjected to stresses caused by ocean currents, waves, transportation, and the like.
Because they have good chemical resistance, good physical properties, light weight, and can be conveniently formed into tubular structures with a variety of cross sections and incorporated into multilayered structures, polyamides are often a desirable material to use for pipes and tubes. However, many marine umbilical applications require that the inner tubes be exposed to nucleophiles such as water and alcohols at elevated temperatures. Under such conditions, the amide bonds of many polyamides may be susceptible to hydrolysis and the rate of hydrolysis increases with temperature. Hydrolysis of the amide bonds can cause a reduction in molecular weight and concomitant loss in physical properties that can result in failure of the pipe during use. Such a failure can be catastrophic, with the loss of fluid causing undesirable consequences ranging from the impairment of the performance of other components present in the umbilical, to contact of the fluid with the external environment if the outer pipe fails.
Aliphatic polyamides such as polyamide 6,12 or polyamide 11 are frequently used to make pipes and tubing, but many applications require greater hydrolysis resistance than can be obtained from currently available polyamides.
It would be desirable to obtain a marine umbilical inner tube component comprising a polyamide composition that has both improved hydrolysis resistance and can be conveniently plasticized to give it the flexibility needed to be useful in many applications. U.S. Pat. No. 6,538,198, which is hereby incorporated by reference herein, discloses a marine umbilical including tubes having an inner polymer sleeve and an outer sleeve of carbon fibers in an epoxy matrix positioned around the inner sleeve.